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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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62                                  ALASKAN GLACIER STUDIES
in some way connected with the flowage of ice under the conditions of expansion into a piedmont bulb of semi-stagnant or stagnant condition.
A flnn.1 feature of note was a narrow depression between morainic ridges which in 1905 and 1906 ran eastward from the base of Lucia Nunatak, for about a half mile. It was much smaller than similar ice-flats seen on Variegated Glacier in 1905 and on Atrevida Glacier in 1909. The development of crescentic ridges and interior flats seems to be a phenomenon common to piedmont ice bulbs, and other instances will be pointed out in the descriptions of other glaciers. Their significance will be discussed in a later chapter after the various instances have been described.
On the western side of Lucia Glacier, almost at the mouth of Floral Pass, a low hill rises between 700 and 750 feet (PI. XVI, B). Russell described it in 1890l as "a huge rounded dome of sandstone rising boldly out of the ice. This is similar to the 'nunataks' of the Greenland ice fields, and was covered by ice when the glaciation was more intense than at present. On the northern side of the island the ice is forced high up on its flanks and is deeply covered with moraines; but on the southwestern side its base is low and skirted by a sandplain deposited in a valley formerly occupied by a lake. The melting of the glacier has in fact progressed so far tittat the dome of rock is free from ice on its southern side, and is connected with the border of the valley toward the west by the sandplain. This plain is composed of gravel and sand deposited by streams which at times became dammed lower down and expanded into a lake. Sunken areas and holes over parts of the lake bottom show that it rests, in part at least, upon a bed of ice."
From its position this hill is useful as a register of changes in the glacier, and for that reason calls for detailed description. In 1905 and 1906 the eastern face of the nunattak was a steep cliff at whose base the glacier flowed in contact with the rock. The northern side, less steeply sloping, was also in contact with the ice, but the southern, or lee slope was free from ice, although the glacier spread westward just below it. On the western side a small ice tongue, or distributary of Lucia Glacier protruded part way down to Floral Pass with a slope of 12, ending in a low, moraine-covered terminus. Thus the hill, which is about f of a mile long and almost half as wide, had ice contact for about half its periphery, while ice was present at a short distance both to the west and south., being absent from less than a quarter of the periphery, toward the southwest. The ice on the northern slope rose more than two-thirds of the way to the top of the nunatak.
Fortunately the junior author made a careful section of the north side of Lucia nunatak in August, 1905. The ice rode up on this stoss side, at an angle of about 22, to a height of 550 feet above the base where there was a rude moraine terrace, 100 yards or so in width, with an ice foundation still present (Fig 4). Above this were two earlier moraines 155 and 50 feet respectively below the top of the nunatak. The lower moraine was about 75 feet wide and the upper contained small lakelets. These 1905 relationships are shown in Pis. XVI, B and XVIII where the 1905 profile is contrasted with that of 1909.
The height to which the ice on the north side of the nunatak rose above the level of the main glacier, in 1905-6, made it seem unlikely that it could have been crowded up to that level by the then-existing thrust of the glacier. The natural inference from this condition is that some recent thrust had pushed the ice up here, and this inference is supported by the fact that for fully 100 feet above the ice the hill slope was barren of
i.Nat. Geog. Mag., Vol. m, 1891, p. 106.